re: What could be causing a young dog to limp that isn't hip dysplasia?

Yes, the drawer test is holding the upper thigh steady and trying to pull the lower leg forward at the "knee" (stifle.) If the CCL is intact, it can't move that way. In a partial tear the changes can be subtle. An x-ray can't show the actual ligament damage but can show inflammation or effusions in the joint.

Surgery is the only way to fix a torn CCL. As a young dog, if you have the means, take her to an orthopedic specialist to get assessed and diagnosed. If it's a CCL tear, even a partial, earlier treatment is best, to reduce those compensatory changes, arthritis, etc.

If it was a small, old dog that is pretty much a couch potato, no real harm in not pursuing a diagnosis or treatment. Some antiinflammatories and dasuquin, adequan, etc might be fine. But in a young active dog, I'd get her diagnosed and fixed up.

Before you schedule any acl surgery, tell the vet to give you a week worth of rimadyl and go home. If your pup, still limps after that, revisit surgery.

Rimadyl saved me $7,500 worth of TPLO surgery the vet was ready to schedule next morning after initial visit.

Full disclosure: 2 year old lab diagnosed with 100% severed acl

Update: I didn't see the specialist that TrueBaldPate recommended, but a second local vet took a look and put my dog through all the tests he could think of today and she passed all of them perfectly. No patellar luxation, no hip dysplasia, no sign of even a partial tear in the CCL. He said it's more in line with a soft tissue injury that she keeps re-injuring through overactivity, which supports what our primary vet suspected. Recommended we rest her up by being pretty restrictive on activity until it clears up.

Thanks to everyone for their input. I asked him about keeping her on cosequin for joint health and he said it's a good idea, so I appreciate that advice as well.